Action Potentials Threshold potential TP Figure 6 21 Vm required to activate Na channels Stimulus then generated by Na influx Weak depolarizations subthreshold potentials AP amplitude aka size if occur Independent of stimulus o The amplitude will always be the same and doesn t depend on how strong or weak the signal is The bullet in a gun will always go the same distance no matter how hard or weak you pull the trigger No change in size not equal to GP Practical application Local anesthetics many block Na channels Propagation down axon Figure 6 23 Adjacent sections of plasma membrane PM o Has action potential but CANNOT move o One starts the next one o Action potential height will ALWAYS be the same height size As distance increases no change in size So no signal changed No distance problem Each action potentials takes 1 2 milliseconds o Unidirectional Not going to trigger backwards Necessary for speed Due to 1 Hyperpolarization Going to need a bigger stimulus to reach the threshold backward whereas going to need a smaller not as big stimulus to reach the threshold forward so it s easier to go keep going forward than go backwards 2 Na channel blocked Propagation down axon Figure 6 24 Myelin insulator o Aids graded potentials GP Usually has a big drop off and decreases quickly but with myelin the drop off is not as large and doesn t decrease as quickly o Blocks action potentials AP Increases conduction velocity Myelin covers some of the section of plasma membrane and makes the action potential move VERY fast Action potentials are triggered and then moves over their graded potentials and continues to trigger the next action potentials o Action potentials AP only at nodes of Ranvier o Jump to next node via graded potentials GP under myelin Has to be a graded potential when traveling through myelin cannot be action potential because there is so much influx Saltatory conduction Back to Chemical Synapses Postsynaptic neuron Figure 6 31 Inputs from multiple presynaptics can occur o Excitatory stimulatory depolarizing Makes it more likely o Inhibitory hyperpolarizing Makes it less likely Temporal summations same close together o One is not enough to reach the threshold o Can send a signal and the receptor ignores and returns to steady state can send two signals back to back and the second will build in strength off of the first one and will be harder to return to steady state bigger result in the postsynaptic closer stimuli in time and postsynaptic cannot return to resting potential before the next one is hit o One child trying to get her attention by tapping her over and over again Spatial summations different close together o Both of her kids sending signals trying to get her attention at the same time o Happens at the same time Synapses can change information more higher complex When there are 4 synapses there are more chances to make her reach threshold than just if there were 2 synapses Can change and make multiple different ways for her to get to the threshold Synapse Strength Figure 6 33 chemical synapse Presynaptic factors Availability of neurotransmitter Ca 2 availability o Did it make enough neurotransmitters to talk to the other cell Need the chemicals for chemical synapse o Not enough calcium then we won t have enough calcium to perform the exocytosis Calcium is very important for bones but even more important for synapse Receptor availability Membrane potential o Most presynaptics are also postsynaptics and they have a message from their receptors so they have receptors to receive messages o Message comes down axon as action potential o Change axon potential Impacts ability to change action potentials and reaching of the threshold potential o Hyperpolarize Makes it harder for message to get through o Depolarize Makes it easier for message to get through Postsynaptic factors Receptor availability Membrane potential o Change in membrane potentials o The starting membrane potential is just as important Other synaptic inputs o Main reason why there will be a change in the membrane potential hyperpolarization and depolarization Anatomy of the Brain Figure 6 39 Cerebral Cortex AKA Cerebrum Cortex outer surface Perception o Problem with eye witness testimonies o Everyone s perceptions are different due how to your brain perceives understands it Voluntary movement of the body o Skeletal muscles under control of cerebrum Language Learning o Can communicate via sounds o Otherwise we would have to redevelop language each and every day Memory Gray matter outer shell o Clustered cell bodies location causes problems since right on the outer surface therefore we have a skull for protection White matter inner layer o Axons myelin is white Myelin is a whole bunch of lipids fats which is all white and therefore this whole area is myelinated axons
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